I saw a shot on Anet only a week or so ago the runway was in sight for the pilots and the photog took a shot with the flash going off.
I'm not sure if he asked the pilots but I'm thinking it wouldn't be a good idea when they are concentrating on the job for a flash to go off.
I wont post the shot but its there.
Cheers

For daytime cockpit shot, there are 3 simultaneus lighting condition that need to be addressed. First, the outside, which will be very bright and requires a high shutter speed. Second, the inside of the cockpit, which will be darker. To address this 2 problems a high-speed sync flash can be used, so both the inside and the outside is properly balanced.

Determine the aperture you want to use, dial it in and take a reading at the brightest spot you can find.
Switch to manual mode and dial in the found value for exposure together with the same aperture.
Turn on the flash light and put it in high speed mode, use it indirect via the ceiling or so.
That's it.

I am sure it's fine..... from 10D onwards as at this time E-TTL was introduced making the "EZ" type obsolete.
It's supports "high speed mode" and is able to tilt as well as rotate, so all you need is there.
Edit2: However now I think about it I think it does not have the extra "wide angle" extension which for example the 550 does have.
For flightdeck shots I use it all the time.[Edited 2006-04-08 23:06:48]

Quoting TWAMD-80 (Reply 10):In that case I'd guess that you have the 550 - how do you like it?

Pretty good.
It does everything I expect from a flash light although I am thinking about getting the new 580 which supports E-TTL2, it seems to work even better.

Quoting TWAMD-80 (Reply 10):The internal flash on the 10D is not really cutting it with the 17-40.

The internal flash is nice for a snap or so but can't be compared to a serious flashlight, it simply lacks the power and can't be aimed in the direction you want.

Quoting Staffan (Reply 11):But if the outside is too bright there's too much difference in luminance between the LCD's and the exterior to fit within one exposure.

That is why you are using a flash light Staffan, to bring the dark and light area's closer together so it does fit.
The Cessna 172 example from Eric Patrick in reply 7 is a good example, very bright outside but still the GPS is perfectly readable.

Quoting TWAMD-80 (Reply 13):When you use a flash for flight deck photos, do you use a diffuser?

Depends on the situation Tim.

Here I used a flashcord so I could keep the flash low in the cockpit and aimed in the direction of the pedals.
In this situation you don't want light to spread around and therefor no wideangle or diff devices were used, just stopped the flash down(-2 if I remember correctly).

Still in the waiting list but nice anyway, working in a cramped space doesn't make it any easier.http://www.airliners.net/addphotos/big/ready/AJSH37_51F21_MG_9809.jpg
So it all comes down to what you want and your own taste, there are many possibilities.
Just don't be afraid to try them and.................... fail
The last example took me probably 5 shots to get it right.

Quoting Aviopic (Reply 12):That is why you are using a flash light Staffan, to bring the dark and light area's closer together so it does fit.
The Cessna 172 example from Eric Patrick in reply 7 is a good example, very bright outside but still the GPS is perfectly readable.